Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.7
Nutrition & Health

"When reared in environments with reduced background levels of ionizing radiation, several species showed depressed growth rates and poor survival (Eugaster 1964, Luckey 1980, 1991, 1994a). For example, reproduction in protozoa was significantly decreased, p < 0.01, (Figure 1) when ionizing radiation was reduced to 25% of ambient levels (Luckey 1986). This result was confirmed in both algae and protozoa (Planel 1987). This is good evidence that ionizing radiation is an essential agent.

"In contrast to the above results, note that added exposures to ionizing radiation increased the growth (reproduction) rates of protozoa (Figure 1) (Luckey 1986). Whole body exposures of mammals to low dose irradiation (doses <10 cGy/y; <10 rad/y) stimulate major physiologic parameters: reproduction, growth, muscular development, mental acuity, cell repair systems (DNA, RNA, membranes and shock proteins), and immune competence (Luckey 1991, Sugahara et al. 1992, Brodsky 1996). This indicates that we live in a partial deficiency of ionizing radiation. Increased immune competence is involved in (1) decreased infection, (2) decreased cancer mortality, and (3) increased average lifespan noted in populations supplemented with low dose irradiation. The decrease in survival and health in environments with reduced radiation contrasted with the benefits derived from increased irradiation indicate that we live with a partial deficiency of ionizing radiation."

"Large and small doses of ionizing radiation evoke opposite biologic effects; this is hormesis (Luckey 1980). Excess radiation, >10 Gy/y (>1000 Rad/y), is harmful. Low dose irradiation, <1 Gy/y (<100 Rad/y), is usually beneficial. The paradigm of radiation hormesis has replaced the "all radiation is harmful" concept; the linear model for the effects of radiation in biology is invalid. Radiation hormesis is reviewed in recent books (Luckey 1991, Kondo 1993, Liu 1996, Brodsky 1996).

"As surely as exposures to excess ionizing radiation cause cancer, it is equally sure that supplementation with low doses decrease cancer mortality rates. Since (1) cancer is such a devastating disease, (2) cancer deaths account for about one fourth of all deaths in this country, and (3) low dose irradiation decreases cancer death rates, cancer mortality rates were used to estimate the minimum yearly radiation allowance (MYRA) for adult males.

"The required information is available from over 300,000 nuclear workers (Table 1). When compared with control nuclear workers, exposed workers consistently had significantly decreased cancer mortality rates, p <0.01, in each plant (Luckey 1994, 1996). The usual "healthy worker effect" was negated by comparing exposed with control nuclear workers in the same plants."

Figure 2.

"Note that the data from experimental animals and human background are expressed in cGy (1 cGy = 1 rad), as in Figure 1 and. Data from worker exposures are measured in cSv (1 cSv = 1 rem), as in Table I and Figure 2. Since most exposures were from either low linear energy transfer (LET) radiation, where the two measures are equivalent, or from radionuclides with short half lives, the biologic component of Sv (rem) is minimized. This allows MYRA to be expressed in cGy (rad)."

"MYRA (Minimum Yearly Radiation Allowance)

"The results from 8 million person-years of experience with nuclear workers (Figure 2) allow estimation of a MYRA for adult males. Although some individual workers received much more, >50 cSv (>50 rem), the dose-response curve was truncated at 7 cSv (7 rem) because the numbers of cancer deaths in workers who received more than 7 cSv (7 rem) was quite small. The highest lifetime exposures used for groups of nuclear workers, 20 cSv (20 rem), resulted in the lowest cancer mortality rates. A conservative evaluation is that 7 cSv (7 rem) represents a minimal beneficial lifetime exposure for these workers.

"At doses considerably higher than 7 cSv (7 rem) the curve must rise through a threshold, the zero equivalent point (ZEP), to a dose which would be harmful. A population exposed to excess irradiation would be expected to have a higher cancer mortality rate than the control population. The ZEP for chronically exposed humans could be obtained from a study of Russian peasants who live near nuclear waste depots in the Tinga River valley."

"Considerations of Time of Exposure

"Should lifetime exposure be considered as a lifetime dose, a dose for the average of 15 years the workers were monitored, a yearly dose, or a shorter time frame? The following information suggests that 7 cSv (7 rem) be considered a yearly rate.

"Most worker exposures were acute from either external radiation or from radionuclides having short half lives. The effects would be dissipated within days. The biologic half life of tritium in humans is 10 days (Eisenbud 1987). Some exposures were from long lived radionuclides which, in minute amounts, are components of our normal background radiation. The biologic half life of uranium is six days in the kidney and 20 days in the skeleton with one component lasting years (Eisenbud 1987). The biologic half life of polonium is 50 days. Plutonium and actinium are very poorly absorbed from the intestine, about 0.1%; however, about 75% of the plutonium inhaled is absorbed (Venugopal and Luckey 1978). Absorbed plutonium deposits mostly in the bones. Thus, the impact of exposures is great for the first weeks following exposure; this diminishes quickly.

"The results from nuclear workers suggest that a MYRA of 7 cSv/y (7 rem/y) would reduce the cancer mortality rate in adult males. A lower suggested allowance was made before the above data were evaluated (Luckey 1995). The theoretic considerations in which an optimum of 10 cSv/y (10 rem/y) was suggested remain valid (Luckey 1991). Thus, the MYRA should be at least 7 cSv/y (7 rem/y) for adult males."

"Collaborative Studies

"Two decades of study of two groups in China, each with 70,000 peasants, suggest improved health, including decreased cancer mortality, p <0.05, in those receiving three times the background radiation level of the controls (Zhai et al. 1982). The cancer death rate was 48.8 per 100,000 peasants living in the high background radiation area; it was 51.1 in the control area. Incidentally, in males over 40 years old the average lifespan of the males in the high background radiation group was statistically longer, p <0.05, than that of the control cohort. This confirms the low total death rate from cancer, cardiovascular and respiratory diseases found in the high radiation Colorado plateau when compared with the population living in the low radiation east coast of the United States (Luckey 1991). These results were verified by the inverse relationship between lung cancer mortality rates and home radon concentrations in the United States (Cohen 1993).

"Other populations have lived with high background radiation for many generations with no obvious problems in health, reproduction or other physiologic parameters (Table 2). Some people in Kerala have much more background radiation, less infertility and fewer neonatal deaths than any other state in India (George et al. 1976) A study of 8,000 couples in Espirito Santo, Brazil, showed people living with high background radiation had normal fertility and fecundity with no unusual congenital abnormalities or stillbirths in 40,000 pregnancies (Freire-Maya and Krieger 1978). Unusual problems were not found in homes having high radiation levels in Iran; generations have lived with lifetime doses of 1,700 cSv (1,700 rem) (Sohrabi 1990). Hanson and Komarov summarized the search for abnormalities in people living in high background radiation areas:

"Although various researchers have looked for them, effects have not been demonstrated regarding cancer mortality (other than malignant neoplasms involving bone), gross congenital abnormalities, fertility index, growth and development, hereditary disease (other than the possibility of Down’s syndrome), infant mortality, longevity, multiple births, sex ratio, or spontaneous abortion rate. (Hanson and Komarov 1983)."

"A heavily contaminated, ‘lethally exposed’, group of 23 Japanese fishermen who were exposed to 2-7 Gy (200-670 rad) from fallout after a hydrogen bomb test on Bikini Island had radiation sickness (white blood cell deficiencies); however, none died from cancer or leukemia within the next 21 years (Kumatori et al. 1980).

TABLE 2. Background Levels of Ionizing Radiation (a)

(a) The United States average is used as a standard (Luckey, 1991).
(b) 1 cGy = 1 rad.
(c) The acute exposure used to displace 200;000 people.
(d) The ZEP, the threshold between beneficial and harmful doses of ionizing irradiation.

"The cancer mortality rate of Japanese atomic bomb victims who were exposed to <7 cGy (<7 rad) was less than that of controls (Shimizu et al. 1992). Children of Japanese atomic bombed parents who had been exposed to <10 cGy (<10 rad) showed only 61% as many phenotypic abnormalities as controls (Schull et al. 1981; Luckey 1991).

"...Infertility was lower and total neonatal mortality was lower in peasants living in the high background radiation area of China than in the controls, p <0.05 (Luckey 1991). Kaplan successfully treated infertile women with exposure of their ovaries to X rays (Kaplan 1949). There were no increased genetic abnormalities of either the children or the grandchildren of the irradiated women (Kaplan 1959). Mole found 30 times less genetic malformations and cancer in prenatally exposed young than in controls (Mole 1979). A well controlled study by Meyer et al. showed women who had been exposed to X rays in utero produced more babies with fewer neonatal deaths than controls, p <0.01, (Meyer et al. 1981). Brent suggested there was no radiation effect in post natal patterns of disease or death (Brent 1983).

"Collaborative studies include the statistically significant, p<0.01, decreased cancer mortality rates in more than 30 experiments with rodents which have been reported in peer reviewed journals (Luckey 1991). The average lifespan of animals exposed to low dose irradiation is consistently and statistically longer than that of controls.

"Mice exposed either acutely or chronically to low dose irradiation had more young than controls. In an extensive study Brown showed low dose irradiation with gamma rays through 15 generations of rats was beneficial during the entire life cycle (Brown 1964). By the usual parameters of reproduction the exposed colony was superior to tire controls: fertility, implantations, number and size of embryos, number, size and growth rate of newborn, and number and weight of weaned pups. These results were confirmed in 24 continuous generations of X ray exposed mice (Stadler and Gowans 1964).

"The mechanisms of increased health following low dose irradiation include

(1) increased immune competence (Bloom et al. 1987; Makinodan 1992, Liu 1992, 1996; Hattori 1994),

(2) cell and organism adaptation (Smith-Sonneborn 1992, Hattori 1995, Liu 1996),

(3) radiogenic metabolism, the activation of metabolic reactions by low dose irradiation (Luckey et al. 1978; Luckey 1980b), and

4) the essential nature of ionizing radiation (Luckey 1994, 1995)."

"Dr. S.-Z. Liu has a modem laboratory devoted to immune competence of irradiated animals (Liu 1992, 1996). Dr. S. Hattori supports about 20 different projects involving radiation hormesis (Hattori 1996). Dr. Sakamoto has pioneered the use of tow dose irradiation in cancer therapy (Sakamoto and Myojin 1996). Some effects of radiation are permanent; Japanese atom bomb survivors showed increased immune competence when compared with controls after a period of 40 years (Bloom et al. 1987)."

"Note that during the 40 year period, 1944-1984, the cancer mortality rate in the United States increased 49%. Arguments can be made about (1) the 1% increased average age per decade, (2) better cancer diagnoses with time, or (3) much of the increase is due to lung cancer.

"However, during this same 40 years the cancer mortality rate of those workers at Oak Ridge National Laboratory who were exposed to <10 cSv (<10 rem) was only 50% that of control workers (Wing et al. 1991). This dramatic comparison shows that supplementation with low doses of ionizing radiation would reverse the trend of increased cancer mortality rate. Low dose irradiation is a negative risk!"